Recent rains have brought the cover crop to life at Trefethen Family Vineyards.
—Recent rains have helped ease the severe drought facing California grapegrowers, but only a little.
The rain fell mainly in California’s North Coast counties of Sonoma, Napa and Mendocino as well as in the central Sierra Nevada, source of most of the water used by growers in the state’s Central Valley.
The central Sierra Nevada snowpack has tripled over the past two weeks, to 36% of average as of Feb. 11, according to the California Department of Water Resources.
The state remains in extreme drought, however.
After nearly two dry months in what is normally a very wet period, the central Sierra snowpack stood at 12%. A storm in late January raised it to 18%, and more snow over the past week brought it to 36%.
The northern Sierra snowpack, the largest source of the state’s water supply, has risen to 19%, while the southern part of the range sits at 26%.
San Joaquin County
Paul Verdegaal, the University of California farm advisor for viticulture, almonds and berries in San Joaquin County, which includes most of the Lodi AVA, said, “Until the past weekend, we were at 10% to 15% of normal. The 2 inches that fell raised us to maybe one-third.”
Lodi averages 17-18 inches per rainfall year (July 1-June 30), with 7-8 inches falling before Jan. 1. “Dry-farmed vines can get by with 18-24 inches, but the growers normally supplement by the equivalent of 6 to 12 inches.”
Verdegaal noted that growers are moving away from deficit irrigation to full irrigation to improve yields.
He added that the recent rains forestalls pre-budding irrigation, which some growers had already started due to the drought.
He pointed out that even though vines are dormant during the usual rainy winter, their roots need to be kept moist or they can die, hampering uptake during the growing season. In addition, the water helps leach salts out of the top portions of the soil.
More growers have been growing cover crops, too, and he estimates they use 20% more water than the vines themselves.
North Coast benefitting
Rhonda J. Smith, the University of California Cooperative Extension viticulture farm advisor for Sonoma County, said that parts of the county received more than 15 inches of rain during the four-day period of Feb. 5-9. In spite of the rain amounts, rainfall totals this year are the lowest recorded in 120 years of data collection. On average, Santa Rosa, Calif., should have received nearly two-thirds of its annual rainfall by now. So far, the city has received less than a third of its 32.22-inch average.
At a meeting Feb 4 in the northern Sonoma County city of Cloverdale, Pam Jeane, an engineer with the Sonoma County Water Agency, said that the current drought is worse than the one in 1977.
She said that the upper Russian River Valley watershed will need a foot of rain over the next three months—combined with a 45% reduction in demand—to return to levels recorded during the 1977 drought.
The county is still considered in a drought. Prior to the rain, the Sonoma County Water Agency had requested a 20% voluntary reduction in water use from the cities it supplies water. They have not reduced that request.
Water supply measured by rainfall, percent capacity of key reservoirs and flow rate into those reservoirs all went up with the rain, but they did little toward bringing levels up to average.
Jeane said, “Before this rain, vineyard ponds that are filled by only sheet flow were nearly dry, and vineyards that relied on those ponds for irrigation were either not going to be able to apply sufficient water or any water in the 2014 growing season. This rainfall helped those growers.”
In Mendocino County, UC farm advisor (and Wines & Vines columnist) Glenn McGourty noted that parts of Mendocino County received between 6 and 12 inches, with high rainfall mostly on coastal ridges. “At the moment, we have about 25% of our normal rainfall, which is normally around 24 inches in Ukiah Valley. This wets the soil in the root zone for many vineyards—a good thing, so growers most likely won’t have to pre-irrigate before bud break, which is something we were facing during our ‘perennial November’ or ‘June-uary.’ It would have been the first time in Mendocino County’s history if that happened.”
McGourty added, “The ‘pump is primed,’ and the tributaries of the Russian and Navarro Rivers are running again. We hope that this is the beginning of a trend, but we are still in a scary place regarding having adequate water to irrigate and frost protect. If we don’t get substantially more rainfall, we will probably be unable to frost protect most of the vineyards that depend on surface water.”
Jon Ruel, president of Trefethen Family Vineyards
and immediate past president of the Napa Valley Grapegrowers, said that Napa Valley received more rain last weekend (Feb 7-9) than in all of calendar year 2013.
The storm brought around 6 inches in Carneros and up to 14 inches on Mt. Veeder.
“On our ranch in the Oak Knoll District we had 7.5 inches, which was probably typical for valley floor locations. That 7.5 inches is about one-fourth of our average annual total. So it was definitely helpful, but obviously we are still well shy of normal.”
He continued, “From a viticultural perspective, the timing of this rain is quite helpful as it comes just before bud break, when vines will use the native soil moisture to push out healthy shoots. In fact, from the vine’s perspective, this will be a wetter start than we had in 2013.”
He cautioned, “Of course, many growers need water to irrigate throughout the summer as well. Fortunately, in much of Napa Valley, we have access to a stable aquifer via wells and that fills our reservoirs, even in the occasional dry year.”
That said , he noted that each grower has his own water situation. “Some depend mostly or entirely on surface water (run-off) to fill their reservoirs. This last rain not only soaked the soil but did also create some surface flow, which allowed some growers to catch much-needed water for storage.”
Ruel added that the ongoing drought has already brought growers together as a farming community and through NVG programs like a recent “town hall” meeting. “We have been exchanging tactics for water conservation and farming during drought conditions.”
“Another thing worth remembering is that we have healthy soils that are able to accept the rain (as opposed to compacted soils), and our strict Hillside Farming Ordinance meant that all vineyards with slopes already had erosion control measures in place, so the heavy rainfall (more than 4 inches Feb. 8) did not create mudslides or other erosion issues.”
He said Napa growers generally use less water because they’re cultivating smaller vines for lower yields and employ practices that keep soil loose and not compacted so it was able to retain the moisture of the recent storm.
Steve Moulds of Moulds Family Vineyard, who is president of the Grapegrowers this year, said, “The rains were a good start, but only that. We will need much more snow in the Sierra to take the pressure off.
“Locally the news is getting better. Our reservoir was in minus condition—that is one foot below the drainpipe before the rains. We are now nearly three-fourths full, remarkably from only one storm. I am confident now with the information shared in a town hall meeting a week ago that we have the tools needed to farm successfully this year.”
He added, “It looks as though we may get at least a few more showers this month, and notwithstanding the dry forecast for the season, the sense of deep concern has passed.”
The Central Coast remains dry
Mark Battany, the University of California Cooperative Extension viticulture/soils farm advisor in San Luis Obispo and Santa Barbara counties, noted that the recent rains were welcome, but they did not make a huge dent in the area’s water deficit. “Most of the rain fell in Northern California. We are still far, far behind a ‘normal’ year on the Central Coast.”
Michael D. Cahn, irrigation and water resources farm advisor for UC Cooperative Extension in Monterey and Salinas counties, said that the recent rains primarily fell in the Santa Cruz Mountains. Not much made it to Monterey County. The major reservoirs in south county are at about 20% of capacity, and the large aquifer under the Salinas Valley is 8 feet below normal on the east side near the Salinas River. The area is totally dependent on local water. It doesn't get any from the Sierra.